The invention relates to an apparatus for folding and flat-sealing the bottom of a liquid-proof package having integral tuck-folded closures, the tubular blank of the package being placed on a mandrel wheel and the folding operation being effected by fold tools having a controlled movement.
Such an apparatus serves as a source of supply for a machine for filling and closing tuck-fold packages made of paper, cardboard or the like. The packages which it processes have on their internal and external surfaces a thermoplastic coating to protect the supporting material of the package against penetration by moisture. The plastic coating simultaneously serves, through appropriate heat treatment and the application of pressure, for sealing the bottom closure of the tubular package blank. Since the plastic coating serves in the areas of the closure for heat sealing as well as moisture-proofing, two factors are important in the achievement of a leak-proof package, namely the so-called "open time," during which the heated plastic coating must remain tacky, and the prevention of the destruction of the heat-softened coating material by the folding tools which move on the surfaces of the folding panels of the package, thus producing attrition.
Sealing machines for the production of bottoms on packages are known, in which tubular package blanks are mounted on the mandrels of a mandrel wheel and this mandrel wheel carries the mounted blanks stepwise to the individual stations equipped with the appropriate processing devices, the bottom parts of the tubular package blank being heated, creased, folded and sealed in the individual steps. This procedure has the disadvantage that, on account of the many steps necessary, a very high initial temperature is needed in order to render the plastic coating tacky, thereby creating the danger of overheating, which might impair the adhesive strength of the coating. Another kind of damage has also frequently been found due to relative movements of the folding tools on the surfaces of the folding panels, since the plastic coating is scraped off by the folding tools. In addition, the working edges of the folding tools become increasingly contaminated and thus no longer assure proper folding action. Also, the necessary cleaning of the tools requires that the machine be shut down. All these disadvantages are ultimately the cause of leaky packages, and they must be eliminated.
The invention is addressed to the problem of performing the folding process in the quickest possible manner, with adequate heating of the carton. In addition, the folding and sealing are to be executed in a single operation so as to prevent the folded panels from changing position during the sealing operation. The most important objective, however, is to avoid damage to the coating and to protect the working edges of the folding tools against contamination by the adhesive coating, so that a uniform, high quality fold will be made, resulting in a liquid-proof package having good stability due to its flat-folded bottom.